1. Field of the Invention
The invention relates to a transdermal therapeutic system, in particular an active substance patch, comprising a detachable protective layer, a pressure-sensitive reservoir layer and a backing layer with or without a coating of pressure-sensitive adhesive. The invention also relates to a process for producing such a transdermal therapeutic system (occasionally abbreviated to TTS below) and to the use thereof.
2. Description of the Prior Art
A TTS is a skin-applied administration form for active substances for delivery through the skin, and has the appearance of traditional patches. It ought to be distinguished from a topical active substance plaster, for example, a rheumatism plaster or a corn plaster. A TTS of this kind can include one or more active substances which are delivered continuously over a fixed period at a predetermined rate to the site of application. (“Heilman Klaus: Therapeutische Systeme—Konzept und Realisation programmierter Arzneiverabreichung” (Therapeutic systems—Design and implementation of programmed drug administration), 4th edition, 1984, Ferdinand-Enke-Verlag, Stuttgart). The fixed period referred to above is usually 24 hours. For the treatment of chronic disorders, however, it is necessary to administer medicaments for a longer period. It may therefore be appropriate to apply a TTS for a period longer than 24 hours, since this is more likely to result in constant plasma levels.
A typical transdermal therapeutic system in the form of a patch is known from EP-B 0 430 019. It has a backing layer which is impermeable to the active substance, a pressure-sensitive adhesive reservoir layer, and a detachable protective layer. The active-substance-impermeable backing layer can be composed of a flexible or inflexible material. Materials such as polymer films, metal foils, or a composite comprising a film which has been coated with aluminum by vapour deposition may be employed as the backing layer. Where such systems are worn on the skin for a prolonged period, in particular for treating chronic disorders, the relative rigidity of the TTS causes a pronounced sensation of a foreign body on the skin within a short period of time. This is extremely unpleasant for the user.
Another embodiment of such a TTS is described in U.S. Pat. No. 5,246,705. The transdermal system it describes has an elastomeric backing layer having a defined vapour transmission rate in the range from 0.1 to 20 g/m2/hr and a Young's modulus in the range of about 104 to 109 dynes/cm2. Particularly, preferred materials for the elastomeric backing layer are, for example, A-B-A block copolymers, the A blocks comprising styrene and the B blocks comprising saturated hydrocarbon polymers such as, for instance, ethylene-butylene copolymers, ethylene-propylene copolymers, and the like. When the transdermal therapeutic systems as per U.S. Pat. No. 5,246,705 are worn on the skin for a prolonged period, it is impossible to avoid the above-described sensation of a foreign body.
U.S. Pat. No. 4,780,168 discloses a strip-like wound bandage for sealing wounds, which is fabricated from a woven or non-woven polymer-based material having a planar stretching characteristic in the range from 0.5 to 110 (pounds/inch). Materials of such extensibility are, however, not immediately suitable as materials for backing layers of transdermal therapeutic systems. Either their extensibility is too low, in which case the aforementioned unpleasant foreign-body sensation is felt when the systems are worn on the skin for a prolonged period, or else they are much too extensible, in which case the production of transdermal therapeutic systems is accompanied by the curling effect, which is explained below.
During the production of the laminate from which the individual active substance patches are punched, the material for the backing layer comes under tensile stress and the resulting elastic return force means that, during punching, the opposite ends of the patches are each bent up. Because of the reject rate during the manufacturing process, the curling effect results in high costs, as well as unnecessary environmental burdens.
Aside from the abovementioned disadvantages, a material for the backing layer of a wound bandage is also unsuited to a TTS for other reasons, such as the required impermeability to the active substance.
The object of the invention is therefore to provide a transdermal therapeutic system which comprises a detachable protective layer, a pressure-sensitive adhesive reservoir layer and a backing layer with or without a coating of pressure-sensitive adhesive and which avoids the aforementioned disadvantages. In particular, there should be no sensation of a foreign body on the skin in the course of prolonged wearing, even for periods of from several days to about 1 or 2 weeks. Furthermore, the production of the TTS should not be accompanied by the curling effect, thus ensuring rational and inexpensive production.
This object is achieved in accordance with the invention by a transdermal therapeutic system, in particular an active substance patch, comprising a detachable protective layer, a pressure-sensitive adhesive reservoir layer and a backing layer with or without a coating of pressure-sensitive adhesive, the backing layer being a unidirectionally, especially longitudinally, elastic material having an elasticity of at least 20%.
Preferred embodiments of the TTS of the invention are the subject-matter of the dependent claims.